1. Field of the Invention
This invention relates to a waveguide structure. More particularly this invention relates to a technique for manufacturing and electrically testing waveguide array units, which have been formed on a wafer in large numbers.
2. Description of the Related Art
Optical waveguides are employed today in optical beam deflectors, electro-optically controllable digital optical switching devices and optical interconnect units. Such devices are known from WO 98/59276, the disclosure of which is herein incorporated by reference.
A known integrated optical interconnect unit 10 employing a waveguide array structure 12 is illustrated in FIG. 1. In this device an input optical fiber 14 provides a beam 16, which impinges on an input lens assembly 18. The input lens assembly 18 provides a multiplicity of focused beams 20. The waveguide array structure 12 is formed on a substrate 22. Each waveguide element 24 of the waveguide array structure 12 receives one of the focused beams 20. Control signals applied to the beams being transmitted through each waveguide element 24 are supplied from a control electronic unit 26 via connector pads 28 and corresponding conductors 30. Having traversed the waveguide array structure 12, the exiting beams 32 are recombined in output optics 34.
Waveguide array structures are conventionally formed as shown in FIG. 2. A waveguide array 36 is carried on the substrate 38. The waveguide array 36 is controlled in an operating optical interconnect device by applying electrical fields along the length of the individual waveguides 40. The waveguide array 36 is conformed to the substrate 38 by etching along scribe lines 42. Electrical integrity of the array structure is therefore essential, and short circuits between the waveguides 40 cannot be tolerated.
Currently the electrical integrity of waveguide arrays is tested once the optical interconnect device has been assembled as an integrated unit. In the event that there has been a manufacturing defect, and an electrical short exists between the waveguide array elements, the entire waveguide array must be replaced, or in some cases the entire assembly must be discarded. This leads to increased cost due to wastage, increased costs of assembly, and delay in manufacturing.
It is therefore a primary object of some aspects of the present invention to provide an improved optical waveguide array structure which can be easily tested for electrical integrity.
It is another object of some aspects of the present invention to reduce the costs of assembling optical devices employing optical waveguide array units.
It is a further object of some aspects of the present invention to increase the reliability of integrated optical waveguide arrays.
These and other objects of the present invention are attained by an improved waveguide structure that allows electrical testing of each unit for shorts between waveguides and shorts between waveguides and the substrate (or ground) prior to assembly into a larger optico-electronic unit. Multiple waveguide array structures are formed on a wafer, each waveguide array structure being provided with a cross bar connected to an electrical contact at each end, such that alternate waveguide elements of the array are electrically connected. When connected to a suitable testing device, the existence of shorts between adjacent elements and shorts between elements and the substrate can be immediately detected. Following testing, the cross bar and electrical contact are removed by scribing.
The invention provides a method of manufacturing an integrated optical structure, comprising the steps of forming a waveguide array, which comprises a plurality of parallel optical waveguides that are spaced apart on a substrate. The waveguides are electrically conductive. The method further comprises electrically interconnecting even numbered waveguides of the waveguide array, electrically interconnecting odd numbered waveguides of the waveguide array, thereafter measuring electrical resistance between the even numbered waveguides and the odd numbered waveguides, and electrically disconnecting the even numbered waveguides from one another, and electrically disconnecting the odd numbered waveguides from one another.
According to an aspect of the invention, forming the waveguide array is performed by applying a mask to a wafer, wherein the mask defines a plurality of waveguide arrays, and a plurality of separable segments adjacent the waveguide arrays.
According to a further aspect of the invention, the step of electrically interconnecting the even numbered waveguides and the step of electrically interconnecting the odd numbered waveguides is performed by applying conductive interconnections on the separable segments, and following the step of measuring electrical resistance, separating the separable segments from the waveguide arrays.
The invention provides a method of manufacturing an integrated optical structure, comprising the steps of forming a waveguide array comprising a plurality of parallel optical waveguides that are spaced apart on a substrate, the waveguides being electrically conductive, electrically interconnecting a first set of the waveguides, electrically interconnecting a second set of the waveguides, thereafter measuring electrical resistance between the first set of the waveguides and the second set of the waveguides, and electrically disconnecting the first set of the waveguides from one another, and electrically disconnecting the second set of the waveguides from one another.
According to an aspect of the invention, the step of forming the waveguide array is performed by applying a mask to a wafer, wherein the mask defines a plurality of waveguide arrays, and a plurality of separable segments adjacent the waveguide arrays.
According to another aspect of the invention, the steps of electrically interconnecting the first set of the waveguides and electrically interconnecting the second set of the waveguides are formed by applying conductive interconnections on the separable segments, and following said step of measuring, separating the separable segments from the waveguide arrays.
The invention provides a method of manufacturing an integrated optical waveguide structure, comprising the steps of forming a waveguide array comprising a plurality of parallel optical waveguides that are spaced apart on a substrate, thereby defining a first group and a second group of optical waveguides, wherein members of the first group alternate on the substrate with members of the second group, disposing ohmic contacts on the waveguides, forming a first electrical interconnection of the first group on the substrate, forming a second electrical interconnection of the second group on the substrate, measuring an electrical resistance between the first electrical interconnect on and the second electrical interconnection, and thereafter removing the first electrical interconnection and the second electrical interconnection.
According to another aspect of the invention, the steps of forming the first electrical interconnection and the second electrical interconnection are performed by forming first extensions of the first group on a first terminal portion of the substrate, forming second extensions of the second group on a second terminal portion of the substrate, forming a first conductive bar across the first extensions, and forming a second conductive bar across the second extensions.
According to an additional aspect of the invention, the step of removing is performed by forming a first scribe line on the first terminal portion, and forming a second scribe line on the second terminal portion, separating the first terminal portion from a central portion of the substrate along the first scribe line, and separating the second terminal portion from the central portion of the substrate along the second scribe lane.
According to an aspect of the invention, the waveguide array includes a plurality of waveguide arrays, and the substrate is common to the waveguide arrays, and a method includes the step of interconnecting each the first electrical interconnection of each of the waveguide arrays.
Yet another aspect of the invention includes the step of interconnecting the second electrical interconnection of each of the waveguide arrays.
The invention provides an optical waveguide array structure, comprising a substrate having formed thereon a plurality of optical waveguides, wherein a first set of alternating ones of the waveguides is extended from a central segment of the substrate onto a first terminal segment of the substrate, a second set of alternating ones of the waveguides is extended from the central segment onto a second terminal segment of the substrate, and a first conductive cross-link is disposed on the first terminal segment connecting the first set of the waveguides.
According to a further aspect of the invention, a second conductive cross-link is disposed on the second terminal segment connecting the second set of the waveguides.
Yet another aspect of the invention, includes a first scribe line disposed between the central segment and the first terminal segment, and a second scribe line disposed between the central segment and the second terminal segment.
According to still another aspect of the invention, the waveguides are parallel.
According to an additional aspect of the invention, the waveguide array includes a plurality of waveguide arrays disposed on the substrate, and a first interconnection between the first conductive cross-link of at least two of the waveguide arrays on the substrate.
According to an aspect of the invention, there is a second interconnection between the second conductive cross-link of the at least two waveguide arrays on the substrate.
The invention provides a method of manufacturing an integrated optical waveguides structure, comprising the steps of forming a waveguide array comprising a plurality of parallel optical waveguides that are spaced apart on a substrate, thereby defining a first group and a second group of optical waveguides, wherein members of the first group alternate on the substrate with members of the second group, disposing first ohmic contacts on the waveguides, disposing a second ohmic contact on the substrate, forming an electrical interconnection of the first group on the substrate, measuring an electrical resistance between one of the first ohmic contacts and the second ohmic contact, and thereafter removing the electrical interconnection.